Advances in brain imaging technologies have made it possible for medical personnel to observe, extract, record, and graphically display electrophysiological signals that reflect brain activity in specific brain regions. These signals may be analyzed to detect many brain-related conditions, including spinal cord injuries, stroke, epilepsy, sleep disorders, brain death, and a variety of brain dysfunctions related to the psychology of a patient ranging from substance abuse to psychosis.
Electrophysiological brain signals are typically recorded by an electroencephalogram (“EEG”) system. The EEG system may be a device that measures the electrical activity in the brain via a multitude of electrodes attached to a patient's scalp by way of a cap or a special glue or paste and connected to the EEG system through wires, called leads. The electrodes detect the electrophysiological signals, and the EEG system amplifies and records them onto paper or computer for analysis by medical personnel.
Recording the EEG signals allows medical personnel to view information (e.g., a graph) reflecting the activity of thousands of neurons in the brain. The pattern of activity in the recorded EEG signals or brain waves changes with the level of the patient's arousal—if the patient is relaxed, the graph shows many slow, low frequency brain waves; if the patient is excited, the graph shows many fast, high frequency brain waves.
While the brain waves provide useful temporal information regarding the electrical activity of the brain, they do not provide the spatial resolution used for determining the exact location of the recorded activity in the brain. High spatial resolution is often important for the diagnosis and treatment of many brain-related conditions such as localized brain tumors and aneurisms.
Higher spatial resolution may be obtained with the use of other brain imaging technologies, including magnetic resonance imaging (“MRI”) and functional MRI (“fMRI”). MRI is a technique that utilizes magnetic and radio frequency (“RF”) fields to provide high quality image slices of the brain along with detailed metabolic and anatomical information. Radio waves 10,000-30,000 times stronger than the magnetic field of the earth are transmitted through the patient's body. This affects the patient's hydrogen atoms, forcing the nuclei into a different position. As the nuclei move back into place they send out radio waves of their own. An MRI scanner picks up those radio waves, and a computer converts them into images, based on the location and strength of the incoming waves.
fMRI is a technique for determining which parts of the brain are activated by different types of physical sensation or activity, such as sight, sound or the movement of a patient's fingers. This is achieved by arranging an advanced MRI scanner in a particular way so that the increased blood flow to the activated areas of the brain shows up on the detailed image slices of the brain.
In order to take advantage of the high temporal resolution of EEGs and the high spatial resolution of MRIs and fMRIs, medical personnel have been increasingly performing simultaneous recordings of EEG and MRI or fMRI data for both medical diagnosis and clinical research. Such simultaneous recording provides the high spatio-temporal resolution needed to study brain activity during different tasks, such as visual, auditory, or motor tasks. Currently, there is no single brain imaging technology that can provide the resolution needed to study this brain activity. The combination of EEGs and MRIs/fMRIs provides the needed resolution, while improving the accuracy of diagnosis of many brain-related conditions.
The combination of these two conventional technologies, however, may provide several safety problems. One such problem involves the integrity of the measurements, as the changing magnetic and RF fields of an MRI/fMRI recording can introduce undesirable artifacts into the EEG recordings. When EEG leads are placed inside an MRI scanner, the rapidly changing RF fields may introduce voltages that obscure the EEG signals. Further, the presence of magnetic materials within the EEG electrodes placed inside the MRI scanner and the electromagnetic radiation emitted by the EEG machine can disturb the homogeneity of the magnetic field, and possibly compromise the quality of the MRI image scans.
The introduction of the EEG equipment into the pulsed RF fields created by the MRI scanner can also present a safety hazard, especially at high static B0 fields because of Specific Absorption Rate (“SAR”) considerations. EEG leads may act as antennas, increasing the patient's exposure to the RF fields. The use of metallic electrodes and leads may cause an undesirable increase in local and whole-head SAR values, reflected in the heating of patient's tissue. Such heating may possibly result in bodily injury to the patient, including burns, electric shock, etc.
Noise can also be introduced into the EEG signals during EEG recording within an MRI scanner. Specifically, noise may be introduced by motion within the MRI environment during the recording of the EEG signals. This motion noise may be associated with a ballistocardiogram motion, e.g., a cardiac pulsation, within the patient, a movement of the patient during the EEG recording, etc. The amplitude of the noise may be approximately of the same magnitude of the EEG signals. Because these motion noises may be present as a direct result of an electromagnetic induction in the magnetic field, the voltage differential between the amplitude of the noise and the amplitude of the EEG signals can increase as the strength of the magnetic field increases.
Several measures have been previously used to alleviate the problems associated with the concurrent use of an EEG machine and the MRI scanner. One such possibility is to replace conventional electrodes with electrodes composed of non-ferromagnetic materials, such as carbon fiber. For example, in U.S. Pat. No. 6,708,051, entitled “FMRI Compatible Electrode and Electrode Placement Techniques,” issued on Mar. 16, 2004, an apparatus for simultaneous EEG/MRI recordings is described as having electrodes and leads that are composed of non-ferromagnetic materials. As described in this U.S. Patent, the electrodes and leads are attached to a stretchable elastic cap fitting the patient's head. It is indicated in this publication that the electrodes and leads provided in the cap may be made of carbon, carbonized plastic or other conductive plastic.
The non-metallic nature of the electrodes and leads makes them less susceptible to induced currents present in the MRI scanner, as well as other artifacts caused by movement of the body within the MRI scanner. However, carbon fibers have a high and fixed conductivity that may not be easily reduced in a cost-effective and commercially feasible manner. The conductivity of the carbon fibers may affect the measurement of the EEG signals. Thus, it is desirable for other materials with lower conductivity to be used as electrodes at least in such arrangement.
Another possibility is to rearrange the EEG equipment leads, so as to connect the electrodes to the EEG recording machine. The placement and alignment of the EEG equipment leads within the MRI scanner can have a substantial impact on the resultant image quality. This is because the EEG leads can interfere with the RF fields within the MRI scanner by de-tuning the coils used in the MRI scanner, thereby resulting in a global attenuation of the received RF signal. For example, U.S. Pat. No. 5,445,162, entitled “Apparatus and Method for Recording an Electroencephalogram During Magnetic Resonance Imaging,” issued on Aug. 29, 1995, describes a system which relocates the EEG machine to a remote and isolated location that is external to the MRI scanner room so as to minimize the interference between the two systems.
Similarly, International Publication No. WO 03/073929, entitled “Electroencephalograph Sensor for Use with Magnetic Resonance Imaging and Methods Using Such Arrangements,” and published on Sep. 12, 2003, describes an EEG recording system which includes an EEG machine which is external to the MRI environment, and that receives the electrical signals via optical fiber between a transmitter located inside the MRI room and a receiver external to the MRI room.
Yet another possibility to address the problems associated with the concurrent use of EEG and MRI machines, and in particular, the motion and other artifact noise that affect the quality of EEG recordings, is to use a filtering system coupled to motion sensors attached to the patient's scalp. Such a system is described in International Publication No. WO 2004/047632, entitled “Apparatus and Method for Ascertaining and Recording Electrophysiological Signals,” and published on Jun. 10, 2004.
While these exemplary measures have assisted in improving the quality of both the EEG and MRI test results, certain problems still exist with such conventional approaches. In particular, there are no methods, systems or arrangements that enable a concurrent recording of that EEG signals and MRI scans, which can simultaneously take into consideration the metallic nature of the electrodes and leads that results in high SAR and RF interferences, the motion and artifact noise within the MRI environment, and the patient safety in general.
Thus, there is a need for methods, systems and arrangements for the delivery and recording of electrophysiological brain signals during MRI that use non-metallic and non-ferromagnetic electrodes and leads.
There is a further need for methods, systems and arrangements to enable delivery and recording of electrophysiological brain signals during MRI that reduce the SAR exposure, while increasing the signal quality and improving patient safety.
There is also a need for methods, systems and arrangements that enable the delivery and recording of electrophysiological brain signals during MRI that reduce the motion and artifact noise within the MRI environment.